It is known that chlorine containing thermoplastics, such as e.g. polyvinyl chloride, split off HCl under thermal load, accompanied by discoloration and degradation.
In order to prevent this so-called thermostabilizers are added, the little poisonous and most effective of which are the organotin mercaptides and the dialkyltin carboxylates.
Those detrimental to health comprise the organometallic compounds of strontium, cadmium and lead.
U.S. Pat. No. 3,644,246 discloses a mixture of dialkyltin carboxylates and sodium, magnesium, calcium or aluminum salts of halfesters of unsaturated dicarboxylic acids, e.g. maleic acid. Beside the formation of anhydride at elevated temperatures there is the disadvantage that stabilizers on this base if combined with phosphites cannot be kept.
According to British Pat. Nos. 1,229,521 and 1,229,522 and Japanese Pat. specification No. 4723442 organotin mercaptides containing calcium, magnesium and barium compounds are proposed. However, it is known that such combinations develop a strong odour during processing.
The present invention is characterized in that the stabilizer compositions contain no tin, lead, cadmium or strontium, whereas also unsaturated dicarboxylic acids, such as maleic acid, are completely absent.
During processing at elevated temperatures no volatile, prickling or strongly smelling substances are developed, and yet the chlorine containing thermoplastics have an effective protection against degradation at elevated temperatures.
Furthermore no "plate out" occurs during processing on calanders.
The combination with liquid organic phosphites is readily possible; they can serve as light stabilizer and solvent.
Addition of solvents such as glycols, glycol ethers and aromatic solvents is not advisable as at elevated processing temperatures odour, volatile vapours and gases develop.
Moreover the stabilizing composition of the present invention may contain anti-oxidants, such as sterically hindered alkyl phenols, such as 2,6-di-tert. butyl-4-methylphenol and 4-hydroxymethyl-2,6-di-tert. butylphenol.
Addition of (2,4-di-tert.butylphenyl)-3,5-di-tert.butyl-4-hydroxybenzoate provides in combination with organic phosphites a substantially increased light resistance.